Production of selective mineral sorbents



Aug. 12, 1958 J. H. ESTES PRODUCTION OF SELECTIVE MINERAL SORBENTS FiledOct. 23, 1956 Unit States Patent Oice Patented Aug. 12, 1958 PRODUCTIONOF SELECTIVE MINERAL SORBENTS John H. Estes, Wappiugers Falls, N. Y.,assiguor to The Texas Company, New York, N. Y., a corporation oiDelaware Application October 23, 1956, Serial No. 617,735

8 Claims. (Cl. 23113) This invention relates to a process for productionof a selective mineral sorbent having the empirical formula Na2O-Al2O32SiO2.ll-5H2O.

This sorbent has the property of selectively sorbing vapors of lowermolecular weight materials such as water, ethane, ethylene, andpropylene from mixtures of the same with larger molecules, e. g.non-straight chain hydrocarbons such as isoparatlinic, isooleiinic,naphthenic, and aromatic hydrocarbons. It is characterized broadly ashaving an effective pore size of approximately 4 Angstrorn units, and,for convenience herein, will be called the 4 A. mineral sorbent. By ionexchanging a proportion of sodium component for certain divalent metalions, e. g. calcium, zinc, cadmium, manganese, or strontium in thestructure of this 4 A. minerai sorbent, the eiicctive pore size can bemade to increase to about 5 Ang strom units. The resulting mineralsorbent,n for convenience herein called a 5 A. mineral sorbent, isuseful in separating higher molecular weight normal psi-radins. olefins,etc. from non-straight chain hydrocarbons, eg. normal butane fromisobutane, normal hexane from isoparafinic hexanes, cyclohexane, andbenzene, etc. ln such process the selective mineral sorbent is contactedwith the hydrocarbon mixture whereby it becomes laden with thestraight-chain material; the laden sorbent can then be stripped, e. g.at elevated temperature with a light gas such as nitrogen, and sorbcdmaterials recovered.

My process produces a highly pure and eiifective 4 A. sodiumalumino-silicate using lowcost commercially available materials. Thisprocess comprises forming a mixture of hydrous silica and by-productsodium salt by reacting an aqueous solution of sodium silicate with asubstance selected from the group consisting of CO2, SO2, H28, thesodium hydrogen salts ot their corresponding acids, and mixtures ofsame; addingI sodium illuminate to said mixture in an amount suflicientto establish the proportions of aluminum and silicon in the resultingmixture essentially stoichiometric for the formulation Na2OAl2O32SiO2;aging the resulting mixture for at least about 8 hours and not more thanabout i60-170 hours at a temperature not substantially above about 100F.; thereafter maintaining the aged mixture under autogenous pressure ata temperature of 150g-325 F. for at least about 3 hours; and recoveringthe hydrated sodium alumino-silicate as the resulting solid fraction.

The particularly useful sodium silicate solutions are broadly 6.5 to 25percent by weight solutions of sodium silicate in water having anequivalent SiO2 concentration of about 5 to about 20 weight percent, andpreferably of about l0 weight percent. The latter solution is made bydiluting one volume of commercial sodium silicate solution having anequivalent SiO2 concentration of about 30 weight percent with twovolumes of water.

Generally, the acidic gas is simply added until the sodium silicatesolution gels. Temperature of the operation can be from about 34 toabout 100 F. When gelation occurs the change is quite sudden, and thetreatment with the acidic gas is discontinued. The acidic gas can bebubbled in as a gas or added as a liquid or solid if available, e. g.CO2 can be added to the solution in the form of Dry Ice. For e'iciencyand economy in practice of my process I prefer to use CO2 and especiallyiiue gases containing CO2 for this operation, but l also can use CO2 andH28 alone, orrnixed, or as components of Waste and title gas streams."`

The gelation step can be accelerated by operating under pressure withmechanical agitation, and further accelerated by treating only one-halfthe sodium silicate solution with the gas until an acid salt by-productis formed, e. g. sodium bicarbonate, bisuliite, and/or acid sulfide,then mixing the reserved portion of the sodium silicate solution withgas-treated portion.

When the hydrous silica has been formed, the required amount of sodiumaluminate is added thereto. The sodium aluminate can be substantiallypure, but the kind I prefer to use is a cheaper material, the commercialgrade of 2NaAlO2-3H2O, a dry solid, which is conven tionally renderedmore soluble in water by the incorpora.- tion therein of about 2-5percent by weight free NaOH. To compensate for the solubilizing quantityof caustic soda so added to the reaction mixture it is necessary, forstoichiometry of the reaction, to add additional hydrous alumina, e. g.a commercially available alumina sol or gel, represented conventionallyby the formula A12O3YH20- Such material can contain up to about 20percent A1203. The reactants are mixed at about room temperature, forconvenience, and a thick creamy reaction mixture is formed. Additionalwater can be .added if desired to facilitate mixing. The proportion ofwater (i. e., tree water and water of hydration) in the reaction mixtureis ad vantageously at least about percent by weight of the totalreaction mixture and is preferably -90 percent.

It is most important that the quantities of reactants used are suilcientto establish proportions of aluminum and silicon in the resultingmixture essentially stoichiometric for the formulation Na2OAl2O3-2Si02,i. e., the molar excess of equivalent silica or alumina in the reactionmixture should not be substantially greater than 5-10 percent. Thereaction mixture, of course, contains some by-product sodium salt formedduring the previous gelation step by the reaction of the sodium silicatewith the gas. This material is not separated, but remains in solutionand assists in the liocculation and filtration of the resultant hydrated4 A. sodium alumino-silicate formed in the subsequent operations.

After the reaction mixture has been made up, it is allowed to stand atroom temperature for at least about 8 hours, and preferably from 24 to72 hours at temperature not substantially above about F., and preferablyat about room temperature. Omission of this aging step results in a lesspure product, perhaps by not allowing the mixture suiiicient time toform the most desirable kind of crystal nuclei. Aging for longer thanabout l60- 170 hours leads to contamination. of the desired 4 A. productwith a material having apparent pore diameter of about 13 A. Use oftemperature substantially above about 100 F. in this aging step defeatsthe aging process by hastening onset of the principal conversion.

After aging, the reaction mixture is maintained at about 15G-280 F. andautogenous pressure for at least about 3 hours, and preferably for about4-24 hours. Reaction time of 4 or more hours appears to give acrystalline particle which is most readily separable from the motherliquor. At temperatures substantially below about F., the reaction issluggish, and above about 325 F. the synthetic sorbent is not likely tobe formed in the desired highly pure state, but rather some analcite, adistinctly inferior selective sorbing material will be formed incontaminating quantities along with other impurities. Preferably thereaction temperature is maintained between 220 F. and 275-280o F. for aperiod of 4-24 hours in a closed reactor whereby water vapors are connedand exert pressure. Steady mechanical agitation of the reaction mixtureduring the heating step is preferred to obtain the purest kind ofproduct, but a quite satisfactory product can be made with littlc or noagitation.

The reaction of sodium silicate with the acid anhydride gas can berepresented by the following equation wherein the acid anhydride gasused is carbon dioxide:

(l) water sodium carbon hydrous sodium silicate dioxide silica CarbonateThe reaction between the hydrous silica so formed and sodium aluminatecan be illustrated as follows:

sodium and hydrated aluminualuminate sodium silicate carbonate Becauseof the solubilizing quantity of free sodium hydroxide conventionallypresent in the sodium aluminate, e. g. about percent of free sodiumhydroxide by weight, it is necessary to add slightly less sodiumaluminate in proportion to the silica gel present than is shown inEquation 2, above, and to make up the difference in thealumina-providing material with hydrous alumina. The reaction of freecaustic soda with hydrous alumina and hydrous silica can be representedby the following equation:

It is most important that the quantities of sodium silicate, sodiumaluminate (and hydrous alumina if the aluminate contains appreciablesolubilizing caustic soda) used be in as closely stoichiometricproportions for the formulation Na2OAl2O32SiO2 as is possible usingconventional metering equipment. Excessive sodium silicate can beeventually converted into free silica which can remain in the reactionproduct, or be converted into compounds such as Na2OA12O3-3SiO2-2H2O orf Na2OAl2O34SiO22H2O (analcite) thus contaminating the end product anddrastically impairing the selectivity of a 5 A. sorbent for straightchain hydrocarbons from mixtures of straight chain and non-straightchain hydrocarbons which is made from such impure 4 A. sorbent product.Excess alumina-providing material, i. e., sodium aluminate and/ orhydrous alumina in the reaction mixture can be converted into severaltypes of free aluminum oxide, depending on the original source of thcalumina-providing material and subsequent treatment of the resulting 4A. sorbent product, and can similarly impair the selectivity of a 5 A.sorbent made therefrom.

After the reaction period at elevated temperature, the subject 4 A.sodium alumino-silicate in a hydrated state is present as a crystallinesolid fraction, and this fraction is separated from the saline motherliquor most simply by filtration. Other solids separation techniquessuch as settling, centrifuging, or the like can be used also to separatethe freshly-formed crystalline solid. The separated solid can be rinsedwith water or an organic solvent such as acetone or alcohol to removeoccluded foreign material. The presence of the by-product sodium salt insolution from the first step of the process assists in separating thishydrated 4 A. crystalline solid by causing tlocculation of thenely-divided particles. The separated solid can be air-driedconveniently to remove dampness from the rinsing to leave the subject 4A. mineral sorbent containing 4-5 molecules of water of hydration.

The separated hydrated 4 A. crystalline material can be virtuallycompletely dehydrated simply by calcining in air at a temperature of 220to l000 F. Use of temperatures substantially above about 1000 F. in thisoperation causes collapse of the structure and loss of selective sorbentproperties. Preferably for efficiency and economy in dehydrating, thetemperature used is 300-600 F. If desired, sub-atmospheric pressure canbe used in the dehydration, but atmospheric pressure calcining ispreferred. It is advantageous during dehydration to sweep water vaporfrom the heater with a current of air or other gas.

The resulting dehydrated mineral sorbent, having the formulaNa2OAl2O3-2SiO2 and containing no appreciable water, is a fine powder.For use in processing of straight chain hydrocarbons these lineparticles are best agglomerated, e. g. by pelleting or extruding througha die with a suitable binder. The line particles can be agglomerated andstabilized for greater strength, for example by processes described inthe following copending U. S. patent applications: Riordan et al.,Serial No. 544,244, filed on November 1, 1955, assigned to The TexasCompany; Hess et al., Serial No. 544,185, filed on November 1, 1955,also assigned to The Texas Company; and Ray, Serial No. No. 599,231,filed on July 20, 1956, assigned to The Texas Company.

The drawing is a reproduction of a typical X-ray diffraction pattern ofa fully hydrated sodium alumina-silicate made by my process. The X-raydiffraction pattern does not agree with that of any of more than 1000natural minerals and synthetic chemicals available for comparison.

The hydrated 4 A. mineral sorbent can be converted into a calcium sodiumalumino-silicate,

having an effective pore size or diameter of about 5 Angstrom units bybase exchanging sodium in the structure for calcium, and thereafterdehydrating as described hereinbefore. In such operation at least 25percent and preferably 40-80 percent of the sodium in the original 4 A.material should be replaced by calcium. A simple way to conduct the baseexchange is to wash the uncalcined mineral sorbent substantially free ofany retained alkali with water and then agitate it for one-half hour totwo days in, for example 0.1-5 N aqueous calcium chloride solution,discarding the calcium chloride solution, and repeating this treatmentwith fresh calcium chloride solution until the necessary proportion ofthe sodium originally present in the structure has been replaced bycalcium. Operating at room temperature and pressure 4-6 changes of 0.1 Ncalcium chloride solution are usually adequate to obtain sufficientcalcium substitution. After calcining, the resulting 5 A. mineralsorbent can be agglomerated and/or stabilized as hereinbefore set forth.

The following examples show ways in which my invention as beenpracticed, and should not be construed as limiting the invention. TheX-ray diffraction patterns of the hydrated sodium alumino-silicatesproduced in each of the following preparations did not differsignificantly from the pattern shown in the drawing.

Example 1.- grams of 40 Baume sodium silicate solution containing 28.5%SiO2, known in the trade as water glass, was diluted with 200 ml. ofwater, then treated with CO2 until a gel of silicic acid formed. 65grams of commercial grade sodium aluminate consisting of 2NaAlO2'3H2Owith 2.85% free NaOH was dissolved in ml. of water. This solution wasmixed thoroughly with the previously-formed silicic acid gelcontainingmixture and 20 grams of alumina hydrogel containing 16% Al2O3. Themixture allowed to stand for 48 hours at room temperature, then heatedin a closed vessel to 250 F. for 16 hours. At the end of this period theresulting crystalline solid fraction was collected by filtration, washedwith water to remove soluble salts, and air dried, this product being100 grams In a modification of the above procedure, sodium bicarbonatewas used as the gelling agent of the diluted sodium solution. Theresulting gel mixture was washed With Water to reduce the sodiumcarbonate content to substantially that of the gel mixture made by thepreparation shown in Example 1. The remainder of the procedure wascarried out in a manner similar to the preparation shown in Example 1.The crystalline solid fraction recovered was like that of Example l.

The procedure of Example 1 can also be modified to utilize sodiumbisuliite and/ or sodium hydrogen suliide as the gelling agent insimilar manner, or to augment the useful acidic gases. However, whensodium salts such as sodium bicarbonate alone or mixed with sodiumbisulfte and/or sodium hydrogen sulfide are used, it is advantageous toextract about 1/3 to 1/2 of the resulting normal sodium salt by-productmade thereby out of the gelled mixture before mixing it with the sodiumaluminate.

Example 2.--100 grams of 40 Baume sodium silicate solution containing28.5% Si02 and known in the trade as Water glass, was diluted with 200ml. of water, then treated with H28 gas until a gel of silicic acidformed. The gelled material was colored somewhat by the impuritiespresent in the commercial silicate solution. 65 grams of a commercialgrade sodium aluminate consisting of 2NaAlO2-3H2O with 2.85% free NaOHwas dissolved in 150 ml. of water. This solution and 20 grams of aluminahydrogel containing 16% A1203 was mixed thoroughly with thepreviously-formed silicic acid gel. The mixture was allowed to stand for48 hours after which it was heated in a closed vessel to 250 F. for 16hours. At the end of this period, the resulting crystalline solidfraction was collected by iiltration, washed with water to removesoluble salts, and air dried, this product being 98 grams of thesynthetic zeolite Nago A1203 45H2O- Example 3.-100 grams of 40 Baumsodium silicate solution containing 28.5% S102 was diluted with 200 ml.of water, then treated with SO2 gas until a gel of silicic acid formed.65 grams of a commercial grade sodium aluminate consisting of2NaAlO2-3H2O with 2.85% free NaOH was dissolved in 150 ml. of water.This solution and 20 grams of alumina hydrogel containing 16% A1303 wasmixed thoroughly with the previously-formed silicic acid gel. Themixture was allowed to stand for 48 hours after which it was heated in aclosed vessel to 250 F. forA 16 hours. At the end of this period, theresulting crystalline solid fraction was collected by ltration, washedwith water to remove soluble salts, and air dried, this product being 95grams of the synthetic zeolite Nago A1203 H20.

Example 4.-100 grams of the 4 A. air-dried synthetic zeolite, made inthe manner of Example 1, was suspended in 600 ml. of aqueous 0.1 N CaCl2solution which had been made alkaline by the addition of a small amountof calcium hydroxide. After minutes of stirring, a sample of thesuspended material was taken for identification, and the remainderresuspended in fresh aqueous 0.1 N CaCIZ solution. A total of sixchanges of solution were made. 'Ihe course of the ion exchange ofcalcium for sodium in the zeolite was observed by a study of the Changesof Solution Isobutane nbutane In the foregoing examples all percentages,unless otherwise specified, are weight percentages.

I claim:

l. A process for production of synthetic crystalline zeolitecharacterized by the empirical formula Nago A1203 and an effective poresize of 4 A. upon dehydration which comprises forming a mixture ofhydrous silica and by-product sodium salt by reacting an aqueoussolution of sodium silicate with at least one substance selected fromthe group consisting of CO2, SO2, H28, sodium bicarbonate, sodiumbisulte, and sodium hydrosultide; adding sodium aluminate to saidmixture in an amount suiiicient to establish the proportions of aluminumand silicon in the resulting mixture stoichiometric for the formulati-onNa2O'Al2O3-2Si02; aging the resulting mixture for 8-170 hours at atemperature not substantially above about F.; thereafter maintaining theaged mixture under autogenous pressure at a temperature of -325 F. forat least about 3 hours; and recovering said crystalline zeolite as theresulting solid fraction.

2. The process of claim 1 wherein said substance is CO2.

3. The process of claim l wherein said substance is 4. The process ofclaim 1 wherein said substance is H28.

5. The process of claim 1 wherein the sodium aluminate used contains asolubilizing quantity of sodium hydroxide, and said solubilizingquantity of sodium hydrox ide is compensated for by incorporatinghydrous alumina into the said resulting mixture.

6. The process of claim 5 wherein the aging of said resulting mixture isdone at about room temperature for about 24-72 hours, and thereaftersaid resulting mixture is maintained between 220280 F. for about 4-24hours.

7. The process of claim 6 wherein the aqueous sodium silicate is reactedwith ue gases.

8. The process of claim 1 wherein said substance is sodium bicarbonate.

References Cited in the le of this patent UNITED STATES PATENTS1,945,838 Vaughan Feb. 6, 1934 UNITED STATES PATENT oEETCE CERTIFICATE@F CRRECTIUN Patent No.. 2,847,280 August l2, 1958 John H Estes It isherebT certified that error appears in theprinted specification of theabove "numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 2, line 6, for "CO2 and H28" read SO2 and HgS Signed and sealedthis 21st day of October 1958.,

SEAL) Attest:

KARL Hf MINE ROBERT C. WATSON Attesting Officer Commissioner of PatentsUNITED STATES PATENT oEEICE CERTIFICATE OE 'CORRECTON Patent No.,2,847,280 August l2, 1958 John H. Estes It is hereb'y certified thaterror appears in theprntsd specification of the above numbered patentrequiring correction and that the said Letters Patent should read ascorrected below.

Column 2, line 6, for n00g and H23 read SO2 and E25 e.

Signed and sealed this 21st day of October 1958.,

(SEAL) Attest:

KARL H, AXLINE ROBERT C. WATSON Attesting Ofcer Commissioner of PatentsUNITED STATES PATENT oEEICE T CERTIFICATE OF -CORRECTION i Patent No.,2,847,280 August l2, 1958 John H., Estes It is hereby certified thaterror appears in the\printed specification of the above l'rmrnheredpatent requiring correction and that the Said Letters Patent should readas corrected below.

Column 2, line 6, for nCO2 and H28 read SO2 and H25 im.

Signed and sealed this 21st day o October 1958.,

SEAL) Attest:

KARL Hf- AXLINE ROBERT C. WATSON Attesting Ofcer Commissioner of Patents

1. A PROCESS FOR PRODUCTION OF SYNTHETIC CRYSTALLINE ZEOLITECHARACTERIZED BY THE EMPIRICAL FORMULA